Tunable rare-earth fcu-metal-organic frameworks

ABSTRACT

Metal organic framework compositions can have a face centered cubic structure.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of Ser. No. 14/019,511, filed on 5Sep. 2013 and which application is incorporated herein by reference. Aclaim of priority is made.

TECHNICAL FIELD

This invention relates to metal-organic frameworks having tunablestructures.

BACKGROUND

Metal-organic framework (MOF) materials can have tunable propertiesbased on their structure, including porosity. Unique porous structurescan allow the material to be used in applications including gassequestration, storage and separation or scrubbing.

SUMMARY

A metal-organic framework composition can have a face centered cubic(fcu) structure. The composition can include a metal ion component and abidentate ligand component having two anionic binding groups. The twoanionic binding groups are oriented 180 degrees from each other. Aplurality of the metal ion component and the bidentate ligand componentassociate to form a 12-connected face-centered cubic network.

A method of making a metal-organic framework composition can includecontacting a metal ion component with a bidentate ligand componenthaving two anionic binding groups, wherein the two anionic bindinggroups are oriented 180 degrees from each other, wherein the metal ioncomponent and the bidentate ligand component associate to form aface-centered cubic network.

In some embodiments, the metal ion component includes a rare earth (RE)metal ion. For example, the rare earth metal ion is La, Ce, Pr, Nd, Sm,Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Tb or Y, for example, terbium (Tb³⁺) oryttrium (Y³⁺).

In some embodiments, the two anionic binding groups can be the same. Insome embodiments, the two anionic binding groups can be the different.In certain circumstances, each of the anionic binding groups,independently, is carboxylate or tetrazolate.

In some embodiments, the two anionic binding groups can be linked by anaromatic group.

In some embodiments, the aromatic group can include a hydrophobic group.For example, the hydrophobic group can be a fluoro group. Thehydrophobic group can assist in the assembly of the fcu structure.

Other aspects, embodiments, and features will be apparent from thefollowing description, the drawings, and the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a drawing representing ball-and-stick and schematicrepresentation of 1: From top to bottom, organic and inorganic MBBs,FTZB²⁻ and the 12-connected Tb-based cluster, respectively, which can beviewed as a linear connection and cuboctahedron node to afford theaugmented fcu net, consisting of octahedral and tetrahedral cages shownas blue and pink truncated polyhedron, respectively, Hydrogen atoms andcoordinated water molecules are omitted for clarity. Tb=green, C=gray,N=blue, O=red, F=purple.

FIG. 2 are graphs representing PXRD patterns for compound 1: (a) afterexposure to water and (b) variable temperature under a vacuum.

FIG. 3 are graphs representing (a) CO₂ data for 1 and 2 at 298 K and (b)Q_(st) in 1 and 2 for CO₂ calculated from the 258, 273 and 298 Kisotherms.

FIG. 4 are graphs representing (a) Q_(st) for CO₂ of compound 1 in sitesI, II, and III compared to the total Q_(st) as determined by the TSLmodel and CO₂ adsorption isotherms of compound 1 for sites I (b), II(c), and III (d) using the TSL model.

FIG. 5 are graphs representing (a) CO₂ selectivity over N₂ resulted fromthe interaction with site I at 298 K at different total pressures in0.5-2.0 bar range calculated using IAST for compound 1 and (b)experimental breakthrough test of traces (1000 ppm) CO₂ in mixture withN₂ on compound 1.

FIGS. 6A and 6B are graphs representing PXRD patterns of theas-synthesized, calculated and solvent-exchanged compounds 1-2,indicating the phase purity of as-synthesized and methanol-exchangedproducts.

FIG. 7 is a graph representing PXRD patterns of the as-synthesized,calculated and solvent-exchanged compound 3, indicating the phase purityof as-synthesized and methanol-exchanged products.

FIGS. 8A and 8B are graphs representing PXRD patterns of theas-synthesized, calculated and solvent-exchanged compounds 4-5,indicating the phase purity of as-synthesized and solvent-exchangedproducts.

FIGS. 9A and 9B are graphs representing PXRD patterns of theas-synthesized, calculated and solvent-exchanged compounds 6-7,indicating the phase purity of as-synthesized and solvent-exchangedproducts.

FIG. 10 is a graph representing PXRD patterns of the as-synthesizedcompounds 1 and 2 compared with the La, Eu and Yb fcu-MOF analogs.

FIG. 11 is a graph representing PXRD patterns for compound 2 afterexposure to water, indicating a highly chemical stability in aqueousmedia.

FIGS. 12A and 12B are graphs representing TGA plots of theas-synthesized and methanol-exchanged compounds 1-2.

FIG. 13 are graphs representing TGA plots of the as-synthesized andmethanol-exchanged compound 3.

FIGS. 14A and 14B are graphs representing TGA plots of theas-synthesized and solvent-exchanged compounds 4-5.

FIGS. 15A and 15B are graphs representing TGA plots of theas-synthesized and solvent-exchanged compounds 6-7.

FIG. 16 is a graph representing variable-temperature (VT) PXRD ofcompound 2, revealing the thermal stability up to 275 degree C.

FIG. 17 is a ball-and-stick representation of compound 1, constructedfrom the assembly of 12-connected carboxylate/tetrazolate-basedmolecular building blocks (MBBs) linked together via a linear andheterofunctional FTZB organic linker, to give a 3-periodic fcu-MOF withtwo types of polyhedral cages: i.e. tetrahedral and octahedral.

FIG. 18 is a ball-and-stick representation of compound 6, constructedfrom the assembly of 12-connected carboxylate-based MBBs linked togethervia a ditopic FBPDC organic linker, to give a 3-periodic fcu-MOF withtwo types of polyhedral cages.

FIG. 19 is a synergetic effect representation of a CO₂ surrounded by anopen metal site, uncoordinated nitrogen atoms of tetrazolate andpolarizable fluoro atom as well as hydroxo moieties.

FIG. 20 are graphs representing Ar sorption isotherms collected at 87 K(a), pore size distribution analysis (b) for compound 1.

FIG. 21 are graphs representing H₂ sorption data for compound 1: (a)fully reversible H₂ isotherms collected at 77 and 87 K and (b) Q_(st)for H₂ calculated from the corresponding isotherms.

FIG. 22 are graphs representing CO₂ sorption data for compound 1: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms

FIG. 23 are graphs representing Ar sorption isotherms collected at 87 K(a), pore size distribution analysis (b) for compound 2.

FIG. 24 are graphs representing H₂ sorption data for data for compound2: (a) fully reversible H₂ isotherms collected at 77 and 87 K and (b)Q_(st) for H₂ calculated from the corresponding isotherms.

FIG. 25 are graphs representing CO₂ sorption data for compound 2: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms.

FIG. 26 are graphs representing CO₂ adsorption isosters for compounds 1(a) and 2 (b), confirming the accuracy of the Q_(st) determined from VTCO₂ adsorption isotherms as evidenced by the linearity in the isosters.

FIG. 27 is a graph representing Q_(st) for CO₂ of compound 2 in sites I,II and III compared to the total Q_(st) as determined by the TSL model.

FIGS. 28A-28C are graphs representing CO₂ adsorption isotherms ofcompound 2 for sites I, II and III using the TSL model.

FIG. 29 are graphs representing Ar sorption isotherms collected at 87 K(a), pore size distribution analysis (b) for compound 3.

FIG. 30 are graphs representing H₂ sorption data for data for compound3: (a) fully reversible H₂ isotherms collected at 77 and 87 K and (b)Q_(st) for H₂ calculated from the corresponding isotherms.

FIG. 31 are graphs representing CO₂ sorption data for compound 3: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms.

FIG. 32 is a graph representing ¹⁹F NMR spectrum of compound 3 digestedin HCl and DMSO, showing the presence of the modulator, 2-fluorobenzoicacid, and thus resulting in a reduced pore volume compared to thetheoretical SCXRD data (i.e. 0.39 vs 0.55 cm³ g⁻¹).

FIG. 33 are graphs representing Ar sorption isotherms collected at 87 K(a), pore size distribution analysis (b) for compound 4.

FIG. 34 are graphs representing H₂ sorption data for compound 4: (a)fully reversible H₂ isotherms collected at 77 and 87 K and (b) Q_(st)for H₂ calculated from the corresponding isotherms.

FIG. 35 are graphs representing CO₂ sorption data for compound 4: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms.

FIG. 36 are graphs representing Ar sorption isotherms collected at 87 K(a) and pore size distribution analysis (b) for compound 5.

FIG. 37 are graphs representing H₂ sorption data for compound 5: (a)fully reversible H₂ isotherms collected at 77 and 87 K and (b) Q_(st)for H₂ calculated from the corresponding isotherms.

FIG. 38 are graphs representing CO₂ sorption data for compound 5: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms

FIG. 39 are graphs representing Ar sorption isotherms collected at 87 K(a), pore size distribution analysis (b) for compound 6.

FIG. 40 are graphs representing H₂ sorption data for compound 6: (a)fully reversible H₂ isotherms collected at 77 and 87 K and (b) Q_(st)for H₂ calculated from the corresponding isotherms.

FIG. 41 are graphs representing CO₂ sorption data for compound 6: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms.

FIG. 42 are graphs representing Ar sorption isotherms collected at 87 K(a), pore size distribution analysis (b) for compound 7.

FIG. 43 are graphs representing H₂ sorption data for compound 7: (a)fully reversible H₂ isotherms collected at 77 and 87 K and (b) Q_(st)for H₂ calculated from the corresponding isotherms.

FIG. 44 are graphs representing CO₂ sorption data for compound 7: (a)fully reversible VT CO₂ isotherms and (b) Q_(st) for CO₂ calculated fromthe corresponding isotherms.

FIG. 45 are graphs representing CO₂ adsorption isosters for compounds 4(a) and 5 (b).

FIG. 46 are graphs representing CO₂ adsorption isosters for compounds 3(a) and 6 (b).

FIG. 47 are graphs representing Q_(st) for CO₂ of compounds 3 (a) and 6(b) in sites I and II compared to the total Q_(st) as determined by theDSL model.

FIG. 48 are graphs representing CO₂ adsorption isotherms of compound 3for sites I and II using the DSL model.

FIG. 49 are graphs representing CO₂ adsorption isotherms of compound 6for sites I and II using the DSL model.

FIG. 50 is a schematic diagram representing the Rubothermgravimetric-densimetric apparatus.

FIGS. 51A-51F are graphs representing excess high-pressure sorptionisotherms for compound 1: H₂, CO₂, CH₄, N₂ and O₂. The adsorption anddesorption branches are represented as solid and open symbols,respectively.

FIG. 52A-52F are graphs representing excess high-pressure sorptionisotherms for compound 2: H₂, CO₂, CH₄, N₂ and O₂. The adsorption anddesorption branches are represented as solid and open symbols,respectively.

FIGS. 53A and 53B are graphs representing water vapor sorption isothermscollected at 298 K for compound 1 (top) and compound 2 (bottom) withadsorption (solid symbols) and desorption (open symbols) points, showingthat both materials are tolerant to water. Note that the last desorptionpoint corresponds to the coordinated water molecules in each material,i.e., 5.50 water per Tb6 cluster and 5.76 water per Y6 cluster.

FIG. 54 is a graph representing CO₂ adsorption kinetics curve forcompound 2 at 0.2 bar and 298 K (collected during adsorptionmeasurements).

FIG. 55 are graphs representing CO₂ selectivity over N₂ resulted fromthe interaction with site I at 298 K at different total pressures in0.5-2 barrange calculated using IAST for compound 1.

FIG. 56 is a graph representing experimental breakthrough test of traces(1000 ppm) CO₂ in mixture with N₂ on compound 1.

FIG. 57 is a graph representing CO₂ over N₂ selectivity for compound 1and 2 calculated using IAST for CO₂/N₂: 10/90 gas mixture at 298 K.

FIG. 58 is a collection of images representing SEM image for compound 1(top), showing the uniform polyhedral morphology of the crystals and theoptical images for compound 3 with different sizes due to varying theethanol concentration during synthesis (bottom).

DETAILED DESCRIPTION

A metal-organic framework composition can have a face centered cubic(fcu) structure composed of metal ions and bidentate ligands. The metalions and bidentate ligands for molecular building blocks that furtherform the fcu structure.

The molecular building block (MBB) approach has recently emerged as apowerful strategy for the design and construction of solid-statematerials. See, e.g., Stein et al., Science 1993, 259, 1558-1564; Ferey,G., J. Solid State Chem. 2000, 152, 37-48; Eddaoudi et al., Science2002, 295, 469-472; Kitagawa et al., Angew. Chem. Int. Ed. 2004, 43,2334-2375; Moulton et al., Chem. Rev. 2001, 101, 1629-1658; Eddaoudi etal., Acc. Chem. Res. 2001, 34, 319-330; and U.S. Pat. No. 6,624,318(each of which is incorporated by reference herein in its entirety). Themolecular building block joins or otherwise associates with othermolecular building blocks to form supramolecular structures. Themolecular building block can be a 12-connected molecular building block.The 12-connected molecular building block can have 12 sites for ligandattachment to neighboring structures.

The metal ions can form a metal ion component of the composition. Themetal ion can be an electron rich metal ion. For example, the metal ioncan be a RE metal ion, for example, a lanthanide elements, such as anion of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or Y. Incertain circumstances, the metal ion is terbium or yttrium, e.g., Tb⁺³or Y⁺³.

The bidentate ligand can form a bidentate ligand component of thecomposition. The bidentate ligand has two anionic binding groups. Thetwo anionic binding groups, point away from each other. Specifically,the two anionic binding groups can be oriented 180 degrees from eachother. The bidentate ligand can have the structure:A1-L-A2  (I)

In formula (I), each A1 can be carboxyl, tetrazolyl, sulfonyl, orphosphoryl;

In formula (I), each A2 can be carboxyl, tetrazolyl, sulfonyl, orphosphoryl;

In preferred embodiments, A1 and A2 are each, independently, carboxyl ortetrazolyl.

In formula (I), L can be a divalent aryl, heteroaryl, carbocyclyl, orheterocyclyl, In preferred embodiments, L can be a 3- to 14 membereddivalent monocyclic heterocyclyl, a 3- to 14 membered divalent aryl, ora 3- to 14 membered divalent heteroaryl. In preferred embodiments, L issubstituted with 1, 2, 3, or 4 halo or halomethyl groups. For example, Lcan be an ortho substituted fluoro phenylene, naphthylene or diphenylenegroup.

The term “aryl” refers to monocyclic, bicyclic or tricyclic aromatichydrocarbon groups having from 6 to 14 carbon atoms in the ring portion.In one embodiment, the term aryl refers to monocyclic and bicyclicaromatic hydrocarbon groups having from 6 to 10 carbon atoms.Representative examples of aryl groups include phenyl, naphthyl,fluorenyl, and anthracenyl.

The term “aryl” also refers to a bicyclic or tricyclic group in which atleast one ring is aromatic and is fused to one or two non-aromatichydrocarbon ring(s). Nonlimiting examples include tetrahydronaphthalene,dihydronaphthalenyl and indanyl.

As used herein, the term “heterocyclyl” refers to a saturated orunsaturated, non-aromatic monocyclic, bicyclic or tricyclic ring systemwhich has from 3- to 15-ring members at least one of which is aheteroatom, and up to 10 of which may be heteroatoms, wherein theheteroatoms are independently selected from O, S and N, and wherein Nand S can be optionally oxidized to various oxidation states. In oneembodiment, a heterocyclyl is a 3-8-membered monocyclic. In anotherembodiment, a heterocyclyl is a 6-12-membered bicyclic. In yet anotherembodiment, a heterocyclycyl is a 10-15-membered tricyclic ring system.The heterocyclyl group can be attached at a heteroatom or a carbon atom.Heterocyclyls include fused or bridged ring systems. The term“heterocyclyl” encompasses heterocycloalkyl groups. The term“heterocycloalkyl” refers to completely saturated monocyclic, bicyclicor tricyclic heterocyclyl comprising 3-15 ring members, at least one ofwhich is a heteroatom, and up to 10 of which may be heteroatoms, whereinthe heteroatoms are independently selected from O, S and N, and whereinN and S can be optionally oxidized to various oxidation states. Examplesof heterocyclyls include dihydrofuranyl, [1,3]dioxolane, 1,4-dioxane,1,4-dithiane, piperazinyl, 1,3-dioxolane, imidazolidinyl, imidazolinyl,pyrrolidine, dihydropyran, oxathiolane, dithiolane, 1,3-dioxane,1,3-dithianyl, oxathianyl, thiomorpholinyl, oxiranyl, aziridinyl,oxetanyl, azetidinyl, tetrahydrofuranyl, pyrrolidinyl,tetrahydropyranyl, piperidinyl, morpholinyl, piperazinyl, azepinyl,oxapinyl, oxazepinyl and diazepinyl.

The term “spiroheterocycloalkyl” as used herein, is a heterocycloalkylthat has one ring atom in common with the group to which it is attached.Spiroheterocycloalkyl groups may have from 3 to 15 ring members. In apreferred embodiment, the spiroheterocycloalkyl has from 3 to 8 ringatoms selected from carbon, nitrogen, sulfur and oxygen and ismonocyclic.

As used herein, the term “heteroaryl” refers to a 5-14 memberedmonocyclic-, bicyclic-, or tricyclic-ring system, having 1 to 10heteroatoms independently selected from N, O or S, wherein N and S canbe optionally oxidized to various oxidation states, and wherein at leastone ring in the ring system is aromatic. In one embodiment, theheteroaryl is monocyclic and has 5 or 6 ring members. Examples ofmonocyclic heteroaryl groups include pyridyl, thienyl, furanyl,pyrrolyl, pyrazolyl, imidazoyl, oxazolyl, isoxazolyl, thiazolyl,isothiazolyl, triazolyl, oxadiazolyl, thiadiazolyl and tetrazolyl. Inanother embodiment, the heteroaryl is bicyclic and has from 8 to 10 ringmembers. Examples of bicyclic heteroaryl groups include indolyl,benzofuranyl, quinolyl, isoquinolyl indazolyl, indolinyl, isoindolyl,indolizinyl, benzamidazolyl, quinolinyl, 5,6,7,8-tetrahydroquinoline and6,7-dihydro-5H-pyrrolo[3,2-d]pyrimidine.

As used herein, the term “carbocyclyl” refers to saturated or partiallyunsaturated (but not aromatic) monocyclic, bicyclic or tricyclichydrocarbon groups of 3-14 carbon atoms, preferably 3-9, or morepreferably 3-8 carbon atoms. Carbocyclyls include fused or bridged ringsystems. The term “carbocyclyl” encompasses cycloalkyl groups. The term“cycloalkyl” refers to completely saturated monocyclic, bicyclic ortricyclic hydrocarbon groups of 3-12 carbon atoms, preferably 3-9, ormore preferably 3-8 carbon atoms. Exemplary monocyclic carbocyclylgroups include, but are not limited to, cyclopropyl, cyclobutyl,cyclopentyl, cyclopentenyl, cyclohexyl or cyclohexenyl. Exemplarybicyclic carbocyclyl groups include bornyl, decahydronaphthyl,bicyclo[2.1.1]hexyl, bicyclo[2.2.1]heptyl, bicyclo[2.2.1]heptenyl,6,6-dimethylbicyclo[3.1.1]heptyl, 2,6,6-trimethylbicyclo[3.1.1]heptyl,or bicyclo[2.2.2]octyl. Exemplary tricyclic carbocyclyl groups includeadamantyl.

As used herein, the term “halocycloalkyl” refers to a cycloalkyl, asdefined herein, that is substituted by one or more halo groups asdefined herein. Preferably the halocycloalkyl can be monohalocycloalkyl,dihalocycloalkyl or polyhalocycloalkyl including perhalocycloalkyl. Amonohalocycloalkyl can have one iodo, bromo, chloro or fluorosubstituent. Dihalocycloalkyl and polyhalocycloalkyl groups can besubstituted with two or more of the same halo atoms or a combination ofdifferent halo groups.

The term “aryl” also refers to a bicyclic or tricyclic group in which atleast one ring is aromatic and is fused to one or two non-aromatichydrocarbon ring(s). Nonlimiting examples include tetrahydronaphthalene,dihydronaphthalenyl and indanyl.

The term “arylalkyl” refers to an alkyl group substituted with an arylgroup. Representative examples of arylalkyl groups include, for example,benzyl, picolyl, and the like.

The term “phenylene” refers to a divalent phenyl.

The molecular building block can include bridging ligands, such as, forexample, oxy, hydroxyl, sulfhydryl, or amino groups.

In the synthesis of the molecular building blocks, the molecularbuilding block can have an overall ionic charge. Thus the molecularbuilding block can be an anion or a cation and have one or morecorresponding counterions, such as, for example, H⁺, Li⁺, Na⁺, K⁺, Mg⁺,Ca²⁺, Sr²⁺, ammonium (including monoalkyl, dialkyl, trialkyl ortetraalkylalkyl ammonium), or one or F⁻, Cl⁻, Br⁻, I⁻, ClO⁻, ClO₂ ⁻,ClO₃ ⁻, ClO₄ ⁻, OH⁻, NO₃ ⁻, NO₂ ⁻, SO₄ ²⁻, SO₃ ²⁻, PO₄ ³⁻, CO₃ ²⁻,borate (including monoalkyl, dialkyl, trialkyl or tetraalkylalkylborate) or PF₆ ⁻, and organic counterions such as acetate or triflate.

The A1 and A2 groups are oriented at 180 degrees from each other. Forexample, when L is arylene, A1 and A2 are in a “para” or substantially“para” relative position. In a phenylene structure, A1 and A2 are atpositions 1 and 4 on the ring; in a biphenylene structure, A1 and A2 areat positions 4 and 4′.

The method of making a MOF composition can include contacting a metalion component with a bidentate ligand component having two anionicbinding groups. A salt of the metal ion can be dissolved in a solventand combined with the bidentate ligand. Optionally, other salts can beadded to provide other counter ions in the final structure. The materialis then crystallized from the combined solution. The presence of ahydrophobic group in the bidentate ligand, for example, a fluoro grouportho to the binding group, contributes to formation of the desired fcustructure. The bidentate ligand having a hydrophobic group can bepresent in a catalytic amount during formation of the final MOF.

A series of fcu-MOFs based on RE metals and linearfluorinated/non-fluorinated, homo-/hetero-functional ligands can betargeted and synthesized. This particular fcu-MOF platform was selecteddue to its unique structural characteristics combined with theability/potential to dictate and regulate its chemical properties (e.g.,tuning of the electron-rich rare-earth metal ions and high localizedcharge density, a property arising from the proximal positioning ofpolarizing tetrazolate moieties and fluoro-groups that decorate theexposed inner surfaces of the confined conical cavities). These featurespermitted a systematic gas sorption study to evaluate/elucidate theeffects of distinctive parameters on CO₂-MOF sorption energetics. Itshows the importance of the synergistic effect of exposed open metalsites and proximal highly localized charge density toward materials withenhanced CO₂ sorption energetics.

In recent years, there has been a strong scientific drive to minimizegreenhouse gas emissions especially CO₂. See, for example, Chu, S.Science 2009, 325, 1599, which is incorporated by reference in itsentirety. The release of CO₂ from flue gas and the automobile industryare the major contributors, and myriad efforts are underway toeconomically separate and capture the effluent CO₂. See, for example,The Center for Climate and Energy Solutions (C2ES), Reducing GreenhouseGas Emissions from U.S. Transportation, 2011, Arlington; Sumida, K.;Rogow, D. L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.;Bae, T.-H.; Long, J. R. Chem. Rev. 2012, 112, 724-781, Vaidhyanathan,R.; Iremonger, S. S.; Shimizu, G. K. H.; Boyd, P. G.; Alavi, S.; Woo, T.K. Science 2010, 330, 650-653, each of which is incorporated byreference in its entirety. Highly porous sorbent materials have emergedas a plausible solution, and considerable efforts have been put forth todevelop suitable materials. An optimal adsorbent for CO₂ separationshould, in addition to high adsorption uptake and suitable kinetics,exhibit high affinity toward CO₂ to be translated into high interaction,which in turns plays a critical role in determining the adsorptionselectivity and the energy required to release CO₂ during theregeneration step. Accordingly, the ideal isosteric heat of adsorption(Q_(st)) should permit reversible physical adsorption-desorptionoperation in a pressure or vacuum swing adsorption (PSA or VSA) process(i.e., CO₂— sorbent interactions are neither too strong nor too weak).

MOFs, a relatively new class of porous materials, appear well-poised toaddress the CO₂ challenge due to their mild synthesis conditions,relatively high thermal stability, large pore volumes, potentiallyexposed inner surface with high localized charge density, and readilyprogrammable and modular construction (i.e., a given structure with thedesired net topology; functionalizable isoreticular structures) frompre-designed molecular building blocks (MBBs). See, for example, Robson,R. J. Chem. Soc., Dalton Trans. 2000, 3735-3744; Férey, G. J. SolidState Chem., 2000, 152, 37-48; Eddaoudi, M.; Moler, D. B.; Li, H.; Chen,B.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34,319-330; Chun, H.; Dybtsev, D. N.; Kim, H.; Kim, K. Chem. Eur. J. 2005,11, 3521-3529; Metal-Organic Frameworks: Design and Application;MacGillivray, L. R., Ed.; Wiley-VCH: Weinheim, Germany, 2010; Kitagawa,S.; Kitaura, R.; Noro, S.-I. Angew. Chem., Int. Ed. 2004, 43, 2334-2375;Ferey, G. Chem. Soc. Rev. 2008, 37, 191-214, each of which isincorporated by reference in its entirety. As such, considerable efforthas been dedicated to ascertaining the ideal CO₂-MOFinteractions/energetics, but minimal systematic studies of finely-tunedMOFs have been reported. See, for example, Sumida, K.; Rogow, D. L.;Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae, T.-H.;Long, J. R. Chem. Rev. 2012, 112, 724-781; Vaidhyanathan, R.; Iremonger,S. S.; Shimizu, G. K. H.; Boyd, P. G.; Alavi, S.; Woo, T. K. Science2010, 330, 650-653, each of which is incorporated by reference in itsentirety.

Development and isolation of novel MBBs can facilitate the rationalconstruction of targeted functional MOFs. See, for example, Liu, Y.;Eubank, J. F.; Cairns, A. J.; Eckert, J.; Kravtsov, V. Ch.; Luebke, R.;Eddaoudi, M. Angew. Chem., Int. Ed. 2007, 46, 3278-3283, each of whichis incorporated by reference in its entirety. The discovery of novelmodular and rigid inorganic MBBs and establishing reaction conditionsthat permit to generate a specific inorganic MBB consistently in situcan be a vital criterion/prerequisite for the prospective design andrational construction of desired MOFs.

With the aim to construct porous MOFs with high localized chargedensity, a potential attribute to promote/enhance the CO₂ sorptionenergetics, porous MOFs with high localized charge density, a potentialattribute to promote/enhance the CO₂ sorption energetics, can beprepared based on metal-ligand directed assembly of electron-rich REmetal ions and non-centrosymmetric hetero-functional ligands containingcarboxylate and terazolate moieties. Hexanuclear RE-based (Tb³⁺/Y³⁺)MBBs, generated in situ, to construct a series of 12-connected MOFs canpossess face centered cubic (fcu) topology. The MBBs are bridged in alinear fashion through an assortment of fluoro and/or tetrazolatefunctionalized organic ligands, as outlined in Scheme 1. Systematic gassorption studies on these materials have elucidated the effects ofdistinctive parameters on CO₂-MOF sorption energetics.

EXAMPLES

A Series of fcu-MOFs Based on Rare-Earth Metals and Functional Ligands

Reactions are based on solvothermal reactions between RE metal salts(RE=Y, Tb) and asymmetric hetero-functional ditopic linkers (e.g.,2-fluoro-4-(1H-tetrazol-5-yl)benzoic acid (H₂FTZB) and4-(1H-tetrazol-5-yl)benzoic acid (H₂TZB)) in various solvent mixtures.Reaction between H₂FTZB and Tb(NO₃)₃.5H₂O in anN,N-dimethylformamide(DMF)/ethanolichlorobenzene solution yieldedtransparent polyhedral crystals, formulated by single-crystal x-raydiffraction (SCXRD) studies as[(CH₃)₂NH₂]₂[Tb₆(μ₃-OH)₈(FTZB)₆(H₂O)₆].(H₂O)₂₂ (1).

Compound 1 crystallizes in the cubic space group Fm-3m. In the crystalstructure of 1, each Tb³⁺ metal ion is surrounded by four μ₃-OH groups,four oxygen and/or nitrogen atoms from statistically disorderedcarboxylate groups and/or tetrazolate rings from four independent FTZB²⁻ligands, leaving the ninth coordination site occupied by a watermolecule (FIG. 1). The adjacent Tb ions are bridged via μ₃-OH anddeprotonated carboxylate and/or tetrazolate groups in a bis-monodentatefashion to give a [Tb₆(μ₃-OH)₈(O₂C—)₆(N₄C—)₆] MBB. Each hexanuclear MBBis bridged through FTZB²⁻ to produce a 3-periodic MOF.

Structural/topological analysis of the resulting crystal structurereveals that 1 is a MOF with the face-centered cubic (fcu) topology(i.e., an fcu-MOF) constructed from the bridged hexanuclear clusters,[Tb₆(μ₃-OH)₈(O₂C—)₆(N₄C—)₆] MBBs, where the carbon atoms of thecoordinated carboxylate and tetrazolate moieties, acting as points ofextension, coincide with the cuboctahedron vertex figure of thequasiregular fcu net, the only 12-connected edge transitive net. Edgetransitive nets possess only one kind of edge, and are ideal targets incrystal chemistry. See, for example, Friedrichs, O. D.; O'keeffe, M.;Yaghi, O. M. Acta Crystallogr. 2003, A59, 22-27; Friedrichs, O. D.;O'keeffe, M.; Yaghi, O. M. Acta Crystallogr. 2003, A59, 515-525;Robinson, S. A. K.; Mempin, M.-V. L.; Cairns, A. J.; Holman, K. T. J.Am. Chem. Soc. 2011, 133, 1634-1637; Masciocchi, N.; Galli, S.; Colombo,V.; Maspero, A.; Palmisano, G.; Seyyedi, B.; Lamberti, C.; Bordiga, S.J. Am. Chem. Soc. 2010, 132, 7902-7904, each of which is incorporated byreference in its entirety. Replacement of the metal salt withY(NO₃)₃.6H₂O in the same reaction mixture, resulted in the analogousfcu-MOF, [(CH₃)₂NH₂]₂[Y₆(μ₃-OH)₈(FTZB)₆(H₂O)₆].(H₂O)₅₂ (2). Similarreaction conditions for the non-fluorinated linker, H₂TZB, resulted inclear solutions. However, introduction of a fluorinated modulator,2-fluorobenzoic acid, has permitted the successful construction of thedesired TZB-based isostructural fcu-MOF,[(CH₃)₂NH₂]₂[Tb₆(μ₃-OH)₈(TZB)₆(H₂O)₆].x(solvent) (3), as determined bySCXRD studies. Under the present reaction conditions, afluoro-substituent located in the alpha (α) position relative to thecarboxylate moiety can be necessary for the formation of the12-connected RE-based MBB. The present hexanuclear clusters, based onmixed carboxylates and tetrazolates, are unprecedented, though acorresponding pure carboxylate molecular cluster based on ceriumrecently appeared in the open literature. See, for example, Mereacre,V.; Ako, A. M.; Akhtar, M. N.; Lindemann, A.; Anson, C. E.; Powell, A.K. Helv. Chim. Acta 2009, 92, 2507-2524; Das, R.; Sarma, R.; Baruah, J.B. Inorg. Chem. Comm. 2010, 13, 793-795, each of which is incorporatedby reference in its entirety.

Occurrence of other analogous hexanuclear clusters in MOF chemistry islimited to a single Zr-based 12-coordinate MBB, where isostructuralZr^(IV)-based fcu-MOFs (e.g., UiO-66) based on [Zr₆(O)₄(OH)₄(O₂C—)₁₂]MBBs are linked together via linear homo-functional dicarboxylateligands. See, for example, Cavka, J. H.; Jakobsen, S.; Olsbye, U.;Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. J. Am. Chem.Soc. 2008, 130, 13850-13851; Schaate, A.; Roy, P.; Godt, A.; Lippke, J.;Waltz, F.; Wiebcke, M. and Behrens, P. Chem. Eur. J. 2011, 17,6643-6651, each of which is incorporated by reference in its entirety.

fcu-MOFs based on RE metals can be constructed, and the[RE₆(μ₃-OH)₈(O₂C—)₆(N₄C—)₆] MBB, RE=Tb and Y can be consistentlygenerated in situ. Such attributes combined with the fact that the fcunet is the only edge transitive net for the assembly of 12-connectedcuboctahedron building units, permit the practice of reticular chemistrypar excellence, rational MOF design, and thus access to a new MOFplatform based on the fcu topology, where the metal ions and ligandfunctional groups and size to perform a systematic study on the effectof the structural changes on CO₂-MOF energetics can be methodicallymodified.

The fcu-MOF structure encloses two polyhedral cages, i.e., octahedraland tetrahedral, with effective accessible diameters estimated to be, inthe case of compound 1, 14.5 and 9.1 Å (considering van der Waalsradii), respectively. Access to the cages is permitted through sharedtriangular windows, ca. 5-6 Å, which are of suitable size for theadsorption of small gas molecules, e.g., Ar, H₂, CO₂, etc. Thecorresponding solvent accessible free volumes for 1 and 2 were estimatedto be 63.0% and 63.8%, respectively, by summing voxels more than 1.2 Åaway from the framework using PLATON software. See, for example, Spek,A. L. Acta Crystallogr. 1990, 46, c34, which is incorporated byreference in its entirety.

In order to achieve maximum and accurate sorption results, the phasepurity of the porous material can first be verified. The phase purity ofthe bulk crystalline materials for 1 and 2 was independently confirmedby similarities between the calculated and as-synthesized powder X-raydiffraction (PXRD) patterns (FIGS. 6A and 6B). In addition, bothcompounds also show favorable water and thermal stability (FIGS. 2, 11and 16), which is an important parameter for potential practicaldeployment of porous MOFs in carbon capture applications.

Argon gas adsorption studies performed on the methanol-exchanged samplesshow fully reversible type-I isotherms, representative of microporousmaterials (FIGS. 20 and 23). The apparent BET surface area and porevolume for 1 and 2 were estimated to be 1220 m² g⁻¹ and 0.51 cm³ g⁻¹,and 1310 m² g⁻¹ and 0.56 cm³ g⁻¹, respectively.

In order to evaluate the performance of compounds 1 and 2, an initial H₂adsorption study at low pressure was performed. The H₂ adsorption uptakewas assessed to be 1.96 and 2.19 wt % at 760 torr and 77 K (FIG. 21(a)and S24(a)), while Q_(st) for H₂ was determined and estimated to be 8.7and 9.2 kJ mol⁻¹ at zero coverage for 1 and 2, respectively (FIGS. 21(b)and 24(b)).

To further this study, the CO₂ sorption was investigated, and it wasfound that 1 and 2 reversibly adsorb a significant amount of CO₂ underambient conditions, i.e., 3.5 mmol g⁻¹ (15.6%) and 4.1 mmol g⁻¹ (18.1%),respectively, at 298 K and 760 torr (FIG. 3(a)). Interestingly and incontrast to most MOFs, a steep slope is observed in the low pressureregion for both materials, a feature that is indicative of enhancedCO₂-MOF interactions. Indeed, the Q_(st) for CO₂ calculated from thecorresponding variable temperature adsorption isotherms was 58.1 and46.2 kJ mol⁻¹, for 1 and 2, respectively, at low loading (FIG. 3(b)). Infact, these results are discerned as amongst the highest reported thusfar for fully reversible CO₂ sorption on MOFs in the absence of anypost-synthetic modification and/or surface area reduction. The accuracyof the Q_(st) determination was confirmed across the entire loadingrange by verifying the linearity of CO₂ adsorption isosters (FIG. 26).At the exception of Mg-MOF-74, the CO₂ uptake at low pressure (0.01 barand 298 K) for 1 and 2 (Table 1) is the highest reported thus far forMOFs (including amine-functionalized MOFs) with relatively fast CO₂adsorption kinetics (FIG. 54).

TABLE 1 CO₂ uptake in compounds 1 and 2 as compared to other MOFsreported in the literature. CO₂ uptake at 0.01 bar Q_(st) at lowcoverage MOFs (mmol g⁻¹) (kJ mol⁻¹) Compound 1 0.33 58.1 Compound 2 0.6246.2 Mg-MOF-74^([a]) 1.5 47 Mmen-Cu BTTri^([b]) 0.023 96^([a])Mg-MOF-74: Caskey, S. R.; Wong-Foy, A. G.; Matzger, A. J. J. Am.Chem. Soc. 2008, 130, 10870-10871. ^([b])Mmen-Cu BTTri: McDonald, T. M.;D'Alessandro, D. M.; Krishna, R.; Long, J. R. Chem. Sci. 2011, 2,2022-2028.

In order to pinpoint and understand the different energetic levelsassociated with the unique CO₂ adsorption properties observed in 1 and2, particularly at low pressures, we performed an in-depth Q_(st)analysis study using a multiple site Langmuir model (MSL). In fact,three energetic sites were clearly identified and derived from the bestfit and convergence obtained when using the triple site Langmuir model(FIG. 27). The observed energies for sites I and III were found to beidentical in 1 and 2, ca. 60 and 25-26 kJ mol⁻¹, respectively. Theformer energetic site can be attributed to the localized highconcentration of charge density resultant from the mutual presence ofboth a fluoro substituent and the nitrogen-rich tetrazolate moiety inproximal vicinity of the open metal site, while site III is simply dueto the effect of pore filling. See, for example, Sumida, K.; Rogow, D.L.; Mason, J. A.; McDonald, T. M.; Bloch, E. D.; Herm, Z. R.; Bae,T.-H.; Long, J. R. Chem. Rev. 2012, 112, 724-781; Lin, J.-B.; Zhang,J.-P.; Chen, X.-M. J. Am. Chem. Soc. 2010, 132, 6654-6656; Lin, Q.; Wu,T.; Zheng, S.-T.; Bu, X.; Feng, P. J. Am. Chem. Soc. 2012, 134, 784-787;Burd, S. D.; Ma, S. Q.; Perman, J. A.; Sikora, B. J.; Snurr, R. Q.;Thallapally, P. K.; Tian, J.; Wojtas, L.; Zaworotko, M. J. J. Am. Chem.Soc. 2012, 134, 3663-3666; Luebke, R.; Eubank, J. F.; Cairns, A. J.;Belmabkhout, Y.; Wojtas, L.; Eddaoudi, M. Chem. Commun., 2012, 48,1455-1457, each of which is incorporated by reference in its entirety.Differences arising from the choice of metal ion are evident in site II,where energetic levels of 47 and 35 kJ mol⁻¹ were determined forcompounds 1 and 2, respectively. The recorded Q_(st) is likely theaverage energy of these sites, while the total CO₂ uptake is thesummation of adsorption isotherms for sites I, II and III (FIGS. 4B-4Dand 28A-28C). The presence of conical pockets (i.e., tripodal andquadrapodal narrow size cavities), decorated with fluoro moieties andtetrazolate groups, can create a high localized charge density andpromote synergetic effects favorable for enhanced CO₂ sorption at lowloadings. Using site I parameters for compound 1, ideal adsorbedsolution theory (IAST; see Myers, A. L. & Prausnitz, J. M. AlChE J. 11,1965, 121-127, which is incorporated by reference in its entirety)prediction of adsorption at various trace concentration of CO₂ (from 100ppm to 1%) in a mixture with N₂, mimicking vacuum swing operational modeat various working pressures, revealed an exceptionally high adsorptionselectivity (ca. 370) for CO₂ over N₂ (FIG. 5A). This finding wasfurther confirmed experimentally using a column breakthrough test with aCO₂/N₂:0.01/99.99% mixture (FIG. 57), showing an even higher selectivity(ca.1051).

The H₂ and CO₂, as well as other gas, sorption properties were furtherinvestigated at high pressure. It was found that at 77 K and 40 bar 1and 2 store 3.9 and 4.4 wt % of H₂, respectively, while for CO₂ 7.1 mmolg⁻¹ (31.2%) and 9.3 mmol g⁻¹ (41.1%) were adsorbed, respectively, at 298K and 25 bar (FIGS. 51A-51F and 52A-52F). Though these values are lowerthan those recorded for Mg-MOF-74, they are among the highest CO₂uptakes per surface unit reported at 25 bar. Markedly, when sites I arefully saturated at lower CO₂ pressures, the less energetic sites (II andIII) dominate the CO₂ adsorption at moderately higher CO₂ concentrationand pressure as reflected by the relatively reduced CO₂/N₂ selectivityto ca. 16 at 10% vs. 370 at 0.01%, as determined by IAST (FIG. 58). Thepredominance of site I, the CO₂ sorption high energetic site, can permitefficient CO₂ separation at intermediate (10%, flue gas) and high(30-50%, biogas) CO₂ concentration.

The successful isolation of reaction conditions that consistently permitthe in situ generation of the [RE₆(μ₃-OH)₈(O₂C—)₆(N₄C—)₆] MBB, andcorresponding fcu-MOF platform, offer potential to assess thedistinctive role of the fluoro substituent and terazolate moiety on theadsorbate-MOF interactions. Accordingly, various analogous/isoreticularfcu-MOFs were targeted and synthesized, including other RE metal ions(e.g., La³⁺, Eu³⁺ and Yb³⁺) (FIG. 10) and diversemono-/poly-fluorinated, hetero-/homo-functional, and extended ligands.

In the first example, the organic linker was expanded from H₂FTZB to3-fluoro-4′-(2H-tetrazol-5-yl)biphenyl-4-carboxylic acid (H₂FTZBP)(Scheme 1) and reacted with Tb or Y nitrate salts to give the expectedisoreticular compounds,[(CH₃)₂NH₂]₂[Tb₆(μ₃-OH)₈(FTZBP)₆(H₂O)₆].x(solvent) (4) or[(CH₃)₂NH₂]₂[Y₆(μ₃-OH)₈(FTZBP)₆(H₂O)₆].x(solvent) (5), respectively. Asexpected, the analogous fluorinated dicarboxylate linker,3-fluorobiphenyl-4,4′-dicarboxylate (FBPDC, Scheme 1), which isgenerated in situ via hydrolysis of4′-cyano-3-fluorobiphenyl-4-carboxylic acid, and3,3′-difluorobiphenyl-4,4′-dicarboxylic acid (H₂DFBPDC, Scheme 1) reactwith Tb to give the isoreticular analog of 1, denoted as[(CH₃)₂NH₂]₂[Tb₆(μ₃-OH)₈(FBPDC)₆(H₂O)₆].x(solvent) (6) and[(CH₃)₂NH₂]₂[Tb₆(μ₃-OH)₈(DFBPDC)₆(H₂O)₆].x(solvent) (7), respectively.The CO₂ sorption properties were assessed for compounds 3-7, and, asexpected, fcu-MOFs constructed from the elongated fluorinatedhetero-functional ligand (i.e., 4 and 5) revealed a lower adsorptioncapacity and reduced Q_(st) values (36.7 and 27.2 kJ mol⁻¹,respectively) compared to the parent fcu-MOF based on the shorter andconjugated FTZB ligand. This study clearly supports that reducing theelectronic density (by increasing the distance between the fluoro andtetrazolate substituents; i.e., by not having both of them on the samephenyl ring) affords a weaker CO₂-framework affinity, which is alsodirectly reflected by the reduced CO₂ uptake. Likewise, 3, 6, and 7,from TZB²⁻, FBPDC²⁻ and DFBPDC²⁻ligands, respectively, have lesslocalized electronic charge density when compared to 1 based on the morepolarized FTZB²⁻ ligand, and thus show reduced CO₂ adsorption uptakesand relatively lower Q_(st) values for CO₂ adsorption at low loading(39.1-46.6 vs 58.1 kJ mol⁻¹ for 1). Additionally, MSL analysis performedon the CO₂ sorption data for 3 and 6 showed that the best fit andconvergence was attained only when the dual site Langmuir was applied(FIG. 48), suggesting the presence of merely two energetic adsorptionsites instead of the three energetic sites originally observed in theparent tetrazolate-based fcu-MOFs (e.g., 1 and 2).

Given the unique structural features of this RE-based fcu-MOF platform,the following synergistic combination of effects is likely responsiblefor the notable CO₂ capacity and high affinity towards CO₂. Theseinclude (i) a high concentration of localized electron-rich vacant metalsites; (ii) the presence of polar groups (i.e., —F, —OH) andnitrogen-rich tetrazolate rings in a confined narrow space and at aproximal vicinity of the open metal sites, favoring multiwall(multi-sites) interactions with a single CO₂ molecule, allowing theirinteraction with CO₂ in a synergistic fashion.

Reaction conditions that consistently permit the in situ generation ofthe RE₆(μ₃-OH)₈(O₂C—)₆(N₄C—)₆] and [RE₆(μ₃-OH)₈(O₂C—)₁₂] hexanuclearMBBs were isolated and successfully employed for the construction of aseries of robust and water stable 12-connected RE-based fcu-MOFs basedon fluorinated/non-fluorinated and hetero-/homo-functional ligands.Trivalent RE metal clusters can be assembled into highly-connected MOFs,in this case fcu-MOFs, displaying diverse adsorption energetics towardCO₂. The utilization of polarized ligands containing tetrazolate andfluoro moieties afforded enhanced sorption energetic and uptakes due totheir unique special positioning, in a narrow proximal vicinity of theopen metal sites, offered by the unique fcu-MOF structure. The high CO₂affinity vs. N₂, particularly at low pressure, as well as the favorabletolerance to water and high thermal stability, certainly renders 1 and 2promising prospective adsorbents for low CO₂ concentration purificationinvolving multicomponent gas adsorption. Studies are underway to furtheremploy the newly isolated 12-connected [[RE₆(μ₃-OH)₈(O₂C—)₆(N₄C—)₆] and[RE₆(μ₃-OH)₈(O₂C—)₁₂] MBBs for the construction of highly connected MOFsbased on hetero-/homo-trifunctional and tetrafunctional ligands with themain objective to increase the concentration per unit surface of thehighly energetic sites for CO₂ sorption in a wide range of pressures.

EXAMPLES

Materials and Methods. The organic ligands used in this study, i.e.,2-fluoro-4-(1H-tetrazol-5-yl) benzoic acid (H₂FTZB) and4-(2Htetrazol-5-yl) benzoic acid (H₂TZB), were synthesized from4-cyano-2-fluorobenzoic acid and 4-cyanobenzoic acid, respectively, with67 and 74% yields using the Demko-Sharpless method.¹⁴ The organic ligand3-fluoro-4′-(2H-tetrazol-5-yl)biphenyl-4-carboxylic acid (H₂FTZBP) wassynthesized from 4′-cyano-3-fluorobiphenyl-4-carboxylic acid accordingto literature methods.¹⁵ The organic ligand3,3′-difluorobiphenyl-4,4′-dicarboxylic acid (H₂DFBPDC) was synthesizedfrom the following Suzuki homocoupling reaction: A mixture of4-borono-2-fluorobenzoic acid (2.0 g, 10 mmol), potassium carbonate (1.5g) and 5% unreduced palladium on carbon (2.0 g) in ethanol (20 mL) washeated at 85° C. for 24 h under nitrogen. The mixture was filteredthrough a Celite pad, and the solvent was evaporated. Five millilitersof 1.0 M sodium hydroxide were added to dissolve the solid. The solutionwas acidified by 1.0 M HCl after filtering and extracted in ethylacetate, dried over Na₂SO₄, and filtered, and the volatiles were removedunder reduced pressure to yield H₂DFBPDC as a white crystalline solid(0.5 g, 36% yield). ¹H NMR (500 MHz, DMF-d7): δ=7.97 (t, J=7.6 Hz, 2H),7.69 (q, J=6.4 Hz, 2H), 7.31-7.39 (m, 2H). All other reagents wereobtained from commercial sources and used without further purification.

Fourier-transform infrared (FT-IR) spectra (4000-600 cm⁻¹) werecollected in the solid state on a Nicolet 700 FT-IR spectrometer. Thepeak intensities are described in each of the spectra as very strong(vs), strong (s), medium (m), weak (w), broad (br) and shoulder (sh).

Powder X-ray diffraction (PXRD) measurements were performed on aPANalytical X′ Pert PRO MPD X-ray diffractometer at 45 kV, 40 mA for CuKα (λ=1.5418 Å) equipped with a variable-temperature stage, with a scanspeed of 2°/min. The sample was held at the designated temperatures forat least 10 min between each scan. High resolution dynamicthermogravimetric analysis (TGA) were performed under a continuous N₂flow and recorded on a TA Instruments hi-res TGA Q500 thermogravimetricanalyzer with a heating rate of 5° C. per minute. Low pressure gassorption measurements were performed on a fully automated Autosorb-1Cgas sorption analyzer (Quantachrome Instruments). High pressure gassorption studies were performed on a magnetic suspension balancemarketed by Rubotherm (Germany). The SEM image was recorded on a Quanta600 FEG scanning electron microscope at 30 kV, and the optical imageswere taken on a CMM-55 microscope. Water vapor sorption measurementswere conducted at room temperature on a VTI-SA symmetrical vaporsorption analyzer. Synthesis of Compounds. Synthesis of Tb-FTZB-MOF (1).

H₂FTZB (13.6 mg, 0.0653 mmol), Tb(NO₃)₃.5H₂O (18.9 mg, 0.0435 mmol), DMF(1.0 mL), C₂H₅OH (0.5 mL), and chlorobenzene (0.5 mL) were combined in a20 mL scintillation vial, sealed and heated to 115° C. for 72 h andcooled to room temperature. The colorless polyhedral crystals werecollected and air dried. FT-IR (4000-600 cm⁻¹): 3379 (br), 1651 (s),1611 (m), 1388 (vs), 1251 (w), 1097 (m), 905 (m), 797 (m), 746 (m), 656(m).

Synthesis of Y-FTZB-MOF (2). H₂FTZB (13.6 mg, 0.0653 mmol), Y(NO₃)₃.6H₂O(16.7 mg, 0.0435 mmol), DMF (1.0 mL), C₂H₅OH (0.5 mL), and chlorobenzene(0.5 mL) were combined in a 20 mL scintillation vial, sealed and wereheated to 115° C. for 72 h. The colorless polyhedral crystals werecollected and air-dried. FT-IR (4000-600 cm⁻¹): 3385 (br), 1658 (s),1612 (m), 1391 (vs), 1204 (w), 1090 (s), 904 (s), 800 (m), 750 (m), 656(m).

Synthesis of Tb-TZB-MOF (3). H₂TZB (16.5 mg, 0.087 mmol), Tb(NO₃)₃.5H₂O(18.9 mg, 0.0435 mmol), 2-fluorobenzoic acid (48.7 mg, 0.348 mmol), DMF(1.0 mL), C₂H₅OH (1.5 mL) were combined in a 10 mL microwave tube,sealed and heated to 115° C. for 72 h and cooled to room temperature.The colorless polyhedral crystals were collected and air-dried. FT-IR(4000-600 cm⁻¹): 3358 (br), 1656 (s), 1603 (vs), 1659 (s), 1497 (w),1397 (vs), 1281 (w), 1255 (w), 1176 (w), 1099 (s), 1058 (w), 1011 (m),878 (w), 840 (w), 801 (m), 751 (s), 701 (w), 663 (w).

Synthesis of Tb-FTZBP-MOF (4). H₂FTZBP (24.7 mg, 0.087 mmol),Tb(NO₃)₃.5H₂O (18.9 mg, 0.0435 mmol), DMF (1.0 mL), C₂H₅OH (0.5 mL), andchlorobenzene (0.5 mL) were combined in a 20 mL scintillation vial,sealed and heated to 115° C. for 72 h and cooled to room temperature.The brown polyhedral crystals were collected and air-dried. FT-IR(4000-600 cm⁻¹): 3358 (br), 1650 (vs), 1610 (m), 1411 (m), 1385 (m),1254 (w), 1099 (s), 1009 (w), 905 (w), 843 (w), 796 (m), 765 (m), 660(w).

Synthesis of Y-FTZBP-MOF (5). H₂FTZBP (24.7 mg, 0.087 mmol),Y(NO₃)₃.6H₂O (16.8 mg, 0.0435 mmol), DMF (1.0 mL), C₂H₅OH (0.5 mL), andchlorobenzene (0.5 mL) were combined in a 20 mL scintillation vial,sealed and heated to 115° C. for 72 h and cooled to room temperature.The brown polyhedral crystals were collected and air-dried. FT-IR(4000-600 cm⁻¹): 3363 (br), 1657 (vs), 1611 (v), 1499 (m), 1412 (m),1385 (s), 1251 (w), 1097 (s), 1058 (w), 1007 (m), 906 (w), 845 (w), 796(m), 765 (m), 660 (w).

Synthesis of Tb-FBPDC-MOF (6). 4-Cyano-3-fluorobiphenyl-4-carboxylicacid (41.9 mg, 0.174 mmol), Tb(NO₃)₃.5H₂O (37.8 mg, 0.087 mmol), DMF(1.5 mL), C₂H₅OH (0.5 mL), and chlorobenzene (0.5 mL) were combined in a20 mL scintillation vial, sealed and heated to 115° C. for 72 h andcooled to room temperature. The colorless polyhedral crystals werecollected and air-dried. FT-IR (4000-600 cm⁻¹): 3350 (br), 1655 (w),1584 (vs), 1528 (w), 1382 (vs), 1188 (w), 1109 (m), 1014 (w), 907 (m),846 (m), 779 (s), 697 (w), 662 (w).

Synthesis of Tb-DFBPDC-MOF (7). H₂DFBPDC (18.2 mg, 0.065 mmol),Tb(NO₃)₃.5H₂O (18.9 mg, 0.0435 mmol), DMF (1.0 mL), C₂H₅OH (0.5 mL), andchlorobenzene (0.5 mL) were combined in a 20 mL scintillation vial,sealed and heated to 115° C. for 60 h and cooled to room temperature.The colorless polyhedral crystals were collected and air-dried. FT-IR(4000-600 cm⁻¹): 3338 (br), 1651 (w), 1582 (vs), 1493 (w), 1528 (w),1385 (vs), 1253 (w), 1209 (w), 1102 (m), 1061 (w), 954 (w), 861 (m), 843(m), 784 (m), 695 (m).

Low-Pressure Gas Adsorption Measurements

Low pressure gas adsorption studies were conducted on a fully automatedmicropore gas analyzer Autosorb-1C (Quantachrome Instruments) atrelative pressures up to 1 atm. The cryogenic temperature was controlledusing liquid nitrogen and argon baths at 77 K and 87 K, respectively.The bath temperature for the CO₂ sorption measurements was controlledusing a recirculating bath containing an ethylene glycol/H₂O mixture.The apparent surface areas were determined from the argon adsorptionisotherms collected at 87 K by applying the Brunauer-Emmett-Teller (BET)and Langmuir models. Pore size analyses were performed using acylindrical/spherical NLDFT pore model system by assuming an oxidic(zeolitic) surface. The determination of the isosteric heats ofadsorption (Q_(st)) for H₂ and CO₂ was estimated by applying theClausius-Clapeyron expression using the H₂ sorption isotherms measuredat 77 K and 87 K and the CO₂ isotherms measured at 258, 273 and 298 Kunless otherwise noted.

Homogenous microcrystalline samples of compounds 1-7 were activated bywashing the as-synthesized crystals with 3×20 mL of DMF followed bysolvent exchange in methanol (Compounds 1-3) or ethanol (compounds 4-7)for 3 days. The solution was refreshed several times daily during thistime period. In a typical experiment, 30 to 40 mg of each activatedsample was transferred (dry) to a 6-mm large bulb glass sample cell andfirstly evacuated at room temperature using a turbo molecular vacuumpump and then gradually heated to 160° C. for 1, 2, 3 and 7, 120° C. for4-5 (increasing at a rate of 1° C./min), held for 16 h and cooled toroom temperature. Data are presented in Table 2.

TABLE 2 Low pressure sorption data summary for compounds 1-7. H₂ CO₂Q_(st) for BET Langmuir P.V. Uptake^(a) Q_(st) for H₂ Uptake^(b) CO₂Compound (m² g⁻¹) (m² g⁻¹) (cm³ g⁻¹) (wt %) (kJ mol⁻¹) (mmol g⁻¹) (kJmol⁻¹) 1 1220 1510 0.51 1.96 8.69-5.39 7.53, 5.86 58.1-75.0 and 3.54 21310 1640 0.56 2.19 9.18-5.68 8.33, 6.46 46.1-24.0 and 4.12 3 904 11450.39 1.47 8.45-5.57 5.96, 4.53 46.6-23.8 and 2.50 4 2200 2560 0.86 1.348.65-5.06 3.93, 2.75 36.7-20.3 and 1.64 5 2410 2820 0.94 1.52 8.52-4.914.01, 2.81 27.2-19.5 and 1.59 6 1940 2330 0.78 1.37 6.84-5.06 3.50, 2.4039.1-18.5 and 1.37 7 1854 2161 0.72 1.36 7.05-4.99 3.91, 2.63 41.6-20.7and 1.36 ^(a)uptake at 77 K and 760 torr; ^(b)= CO₂ uptake measured at258, 273 and 298 K respectively.

CO₂ Adsorption Q_(st) Analysis on Compounds 1 and 2 Using Multiple-siteLangmuir model (MSL)n=n _(sat1) *b ₁ p/1+b ₁ p+n _(sat2) *b ₂ p/1+b ₂ p+ . . . +n _(sati) *b_(i) p/1+b _(i) p  Equation for MSL:

The best fit and convergence were obtained with the triple site Langmuir(TSL) model. The parameters extracted from the best TSL fit were used torecalculate the adsorption isotherms and the evolution of the Q_(st) foreach energetic site (site I, site II and site III) using theClausius-Clapeyron equation.

TABLE S2 Triple site Langmuir parameters (Compound 1) Temperature/KParameters 258 273 298 Adsorption n_(sat1) 0.33956 0.27756 0.26915 SiteI b₁ 147.49445 48.15585 5.50219 Adsorption n_(sat2) 0.37026 0.401040.42827 Site II b₂ 4.91024 1.58224 0.22432 Adsorption n_(sat3) 10.8653911.18523 15.24316 Site III b₃ 0.01703 0.00865 0.00231

TABLE S3 Triple site Langmuir parameters (Compound 2) Temperature/KParameters 258 273 298 Adsorption n_(sat1) 0.39195 0.35252 0.29521 SiteI b₁ 259.98806 80.03201 23.96898 Adsorption n_(sat2) 0.52812 0.53340.62601 Site II b₂ 9.75852 2.64722 0.83725 Adsorption n_(sat3) 11.8240212.0789 12.99557 Site III b₃ 0.01696 0.00859 0.00326

High-Pressure Gas Adsorption Measurements

Adsorption equilibrium measurements for the pure gases were performedusing a Rubotherm gravimetric-densimetric apparatus (Bochum, Germany)(FIG. 50), composed mainly of a magnetic suspension balance (MSB) and anetwork of valves, mass flowmeters and temperature and pressure sensors.The MSB overcomes the disadvantages of other commercially availablegravimetric instruments by separating the sensitive microbalance fromthe sample and the measuring atmosphere and is able to performadsorption measurements across a wide pressure range, i.e. 0 to 200 bar.Moreover, the adsorption temperature can be controlled in the range of77 K to 423 K. In a typical adsorption experiment, the adsorbent isprecisely weighed and placed in a basket suspended by a permanent magnetthrough an electromagnet. The cell in which the basket is housed is thenclosed and vacuum or high pressure is applied. The gravimetric methodallows the direct measurement of the reduced gas adsorbed amount Ω.Correction for the buoyancy effect is required to determine the excessadsorbed amount using equation 1, where V_(adsorbent) and V_(ss) referto the volume of the adsorbent and the volume of the suspension system,respectively. These volumes are determined using the helium isothermmethod by assuming that helium penetrates in all open pores of thematerials without being adsorbed. The density of the gas is determinedusing Refprop equation of state (EOS) database and checkedexperimentally using a volume-calibrated titanium cylinder. By weighingthis calibrated volume in the gas atmosphere, the local density of thegas is also determined. Simultaneous measurement of adsorption capacityand gas phase density as a function of pressure and temperature istherefore possible. The excess uptake is the only experimentallyaccessible quantity and there is no reliable experimental method todetermine the absolute uptake. For this reason, only the excess amountsare considered in this work.Ω=m _(excess)−ρ_(gas)(V _(absorbant) +V _(ss))  (1)

The pressure is measured using two Drucks high pressure transmittersranging from 0.5 to 34 bar and 1 to 200 bar, respectively, and one lowpressure transmitter ranging from 0 to 1 bar. Prior to each adsorptionexperiment, about 100 mg to 300 mg sample is outgassed at 433 K at aresidual pressure 10⁻⁴ mbar. The temperature during adsorptionmeasurements is held constant by using a thermostated circulating fluid.

FIG. 55 shows the selectivity of CO₂ over N₂ at 298 K, calculated (usingIAST)[c] from levels of a few ppm to 1%, assuming CO₂ interaction withcompound 1 are completely governed by adsorption on site I. Theselectivity was calculated assuming different total pressures for themixtures (i.e., 0.5, 1 and 2 bar). The purpose of the total pressurevariation is to mimic vacuum swing adsorption (VSA) regeneration modeconditions supposing 0.2, 0.5 and 1 bar as the working adsorptionpressure and vacuum as the desorption pressure. As was expected, the CO₂selectivity over N₂ was high (ca. 370) in the domain when interactionwith site I are the most dominant. Prediction of CO₂/N₂ selectivity atvariable total pressures from 0.5 bar and up to 2 bar showed that theCO₂/N₂ separation decreased by increasing the total pressure andconcentration due to the quick saturation of most of energetics sites(site I) available. Therefore a way to maintain high selectivity is toincrease the density of site I. In order to confirm this finding,breakthrough adsorption experiments were carried out using a CO₂/N₂mixture containing 1000 ppm of CO₂ at 298 K and a total pressure of 1bar. The purpose of using such low concentration is to exploreexperimentally the separation performance of the compound 1 where theadsorption is mostly governed by the most energetic site (site I).

Interestingly, the breakthrough test shows that the CO₂ was retained inthe bed for ca. 5250 s while N₂ breakthrough occurred almost after fewsecond (FIG. 56). The gas uptake for CO₂ and N₂ at breakthrough was0.262 and 0.249 mmol/g. Therefore, the CO₂/N₂ selectivity wasexceptionally high (ca. 1051) exceeding the predicted selectivity usingIAST. This finding is extremely important as it shows that materialswith high density of adsorption site I will certainly lead to suitableseparation agents for CO₂ removal from gas streams with even higher CO₂concentration (10-30%) in order to produce useful commodities such asCH₄, O₂ and H₂ with higher efficiency. Ongoing work is focusing on thedesign of new MOFs with such attributes.

Single Crystal X-ray Crystallography. Single-crystal X-ray diffractiondata were collected using a Bruker-AXS SMART-APEX2 CCD diffractometer(Cu Kα, λ=1.54178 Å) for compounds 1 and 2, Bruker X8 PROSPECTOR APEX2CCD (Cu Kα, λ=1.54178 Å) for compounds 3 and 5-7, and Oxford SupernovaAtlas CCD (Mo Kα=0.71073 Å) for compound 4. Indexing was performed usingAPEX2 (Difference Vectors method). 16 Data integration and reductionwere performed using SaintPlus 6.01. Bruker SAINT, Data ReductionSoftware; Bruker AXS, Inc.: Madison, Wis., 2009, which is incorporatedby reference in its entirety. Absorption correction was performed bymultiscan method implemented in SADABS. Sheldrick, G. M. SADABS, Programfor Empirical Absorption Correction; University of Gottingen: Gottingen,Germany, 2008, which is incorporated by reference in its entirety. Spacegroups were determined using XPREP implemented in APEX2. Bruker APEX2;Bruker AXS, Inc.: Madison, Wis., 2010, which is incorporated byreference in its entirety. Structures were solved using SHELXS-97(direct methods) and refined using SHELXL-97 (full-matrix least-squareson F2) contained in APEX216 and WinGX v1.70.01 programs packages. See,for example, (a) Farrugia, L. J. Appl. Crystallogr. 1999, 32, 837-838,and Sheldrick, G. M. SHELXL-97, Program for the Refinement of Crystal;University of Gottingen: Gottingen, Germany, 1997. (c) Sheldrick, G. M.Acta Crystallogr. 1990, A46, 467-473. (d) Sheldrick, G. M. ActaCrystallogr. 2008, A64, 112-122, each of which is incorporated byreference in its entirety. CrysAlis Pro package was used to processdiffraction images for compound 4. CrysAlis Pro; Oxford Diffraction:Abingdon, U.K., 2009, which is incorporated by reference in itsentirety. For all compounds the ligand moiety was disordered and atomswere refined using geometry restraints. Restraints were also used torefine anisotropic displacement parameters of disordered atoms.Disordered cations and solvent molecules were refined isotropically.Relatively high residual electron density observed in a μ-OH position(leading to very small value of thermal parameteres for μ-OH oxygen) aremost likely attributed to “electron transfer ( . . . ) directed fromd-orbitals to the oxygen 2p orbitals”, which is observed inyttrium-oxide clusters. Pramann, A.; Nakamura, Y.; Nakijama, A.; Kaya,K. J. Phys. Chem. A 2001, 105, 7534-7540, which is incorporated byreference in its entirety. Hydrogen atoms were placed in geometricallycalculated positions and included in the refinement process using ridingmodel with isotropic thermal parameters: U_(iso)(H)=1.2 Ueq (—OH, —CH).

The crystal of compound 7 was twinned, twinning law [−0.66/−0.33/0.66][0.66/−0.66/0.33][0.33/0.66/0.66]. Two reciprocal lattices have beenidentified using XPREP (APEX2); diffraction data have been integratedusing SAINT and scaled/corrected using TWINABS. Sheldrick, G. M.TWINABS; Bruker AXS, Inc.; Madison, Wis., 2002, which is incorporated byreference in its entirety. Refinement has been carried using HKLF 5style reflection data containing reflection from both domains(BASF=0.12). Distance restraints have been used to refine disorderedbenzene rings.

Disordered atoms have been refined isotropically. For compounds 3-7, thecontribution of heavily disordered solvent molecules was treated asdiffuse using Squeeze procedure implemented in Platon program. Spek, T.L. Acta Crystallogr. 1990, A46, 194-201, which is incorporated byreference in its entirety. Crystal data and refinement conditions areshown in Tables 3-11.

TABLE 3 Selected Low Pressure Sorption Data for Compounds 1-7 compound 12 3 4 5 6 7 BET (m² g⁻¹) 1220 1310 904 2200 2410 1940 1854 PV (cm³ g⁻¹)0.51 0.56 0.39 0.86 0.94 0.78 0.72 CO₂ uptake^(a) 7.53, 5.86, and 8.33,6.46, and 5.96, 4.53, and 3.93, 2.75, and 4.01, 2.81, and 3.50, 2.40,and 3.91, 2.63, and (mmol g⁻¹) 3.54 4.12 2.50 1.64 1.59 1.37 1.36 Q_(st)for CO₂ 58.1-25.0 46.1-24.0 46.6-23.8 36.7-20.3 27.2-19.5 39.1-18.541.6-20.7 (kJ mol⁻¹) ^(a)CO₂ uptake at 760 Torr measured at 258, 273,and 298 K, respectively.

TABLE 4 Selected Crystallographic Data and Structural Refinement forCompounds 1-7 compound 1 2 3 4 formula C₅₂H₁₈Tb₆N₂₆O₄₈F₆C₅₂H₁₈Y₆N₂₆O₇₈F₆ C₄₈H₃₂Tb₆N₂₄O₅₈ C₈₄H₄₂Tb₆N₂₄O₂₆F₆ FW (g mol⁻¹) 2842.442902.38 2826.43 2870.94 crystal system cubic cubic cubic cubic spacegroup Fm3m Fm3m Fm3m Fm3m a (Å) 23.5553 (2) 23.4365 (4) 23.5195 (5)29.5957 (3) V (Å³) 13069.7 (2) 12873.0 (4) 13010.2 (5) 25923.0 (5) Z,D_(cal) (g cm⁻³) 4, 1.445 4, 1.498 4, 1.439 4, 0.736 θ_(max) (°) 65.7463.48 67.93 28.27 R_(int) 0.0610 0.0313 0.0380 0.0289 R₁ (I > 2σ(I₀))0.0359 0.0395 0.0340 0.0236 wR₂ (all data) 0.1315 0.1183 0.1031 0.0724GOF 1.099 1.052 1.086 1.072 Δρ_(max)/Δρ_(min) 1.559/−0.396 1.849/−0.5971.161/−0.493 1.128/−0.532 (e · Å⁻³) compound 5 6 7 formulaC₈₄H₄₂Y₆N₂₄O₂₆F₆ C₈₄H₄₂Tb₆O₃₈F₆ C₈₄H_(36 Tb) ₆O₄₆F₁₂ FW (g mol⁻¹)2450.88 2726.70 2962.65 crystal system cubic cubic cubic space groupFm3m Fm3m Fm3m a (Å) 29.447 (3) 27.5127 (12) 27.4756 (7) V (Å³)  25535(4) 20825.7 (16) 20741.6 (9) Z, D_(cal) (g cm⁻³) 4, 0.638 4, 0.870 4,0.949 θ_(max) (°) 65.64 63.44 67.93 R_(int) 0.0198 0.0442 0.000 R₁ (I >2σ(I₀)) 0.0337 0.0402 0.0732 wR₂ (all data) 0.1016 0.1125 0.2085 GOF1.059 1.051 1.051 Δρ_(max)/Δρ_(min) 0.675/−0.283 0.839/−0.7161.137/−1.339 (e · Å⁻³)

TABLE 5 Crystal data and structure refinement for compound Tb-FTZB-MOF(1) Identification code 1 Empirical formula C₅₂ H₁₈ F₆ N₂₆ O₄₈ Tb₆Formula weight 2842.44 Temperature 100(2) K Wavelength 1.54178 Å Crystalsystem, space group Cubic, Fm-3m Unit cell dimensions a = 23.5553(2) Åalpha = 90 deg. b = 23.5553(2) Å beta = 90 deg. c = 23.5553(2) Å gamma =90 deg. Volume 13069.71(19) Å³ Z, Calculated density 4, 1.445 Mg/m³Absorption coefficient 16.373 mm⁻¹ F(000) 5360 Crystal size 0.10 × 0.10× 0.10 mm Theta range for data collection 5.31 to 65.74 deg. Limitingindices −19 <= h <= 26, −27 <= k <= 27, −27 <= l <= 24 Reflectionscollected/unique 14184/637 [R(int) = 0.0610] Completeness to theta =65.74 99.4% Absorption correction Semi-empirical from equivalents Max.and min. transmission 0.2913 and 0.2913 Refinement method Full-matrixleast-squares on F² Data/restraints/parameters 626/57/81 Goodness-of-fiton F² 1.099 Final R indices [I > 2sigma(I)] R₁ = 0.0359, wR₂ = 0.1294 Rindices (all data) R₁ = 0.0401, wR₂ = 0.1315 Largest diff. peak and hole1.559 and −0.396 e.Å⁻³

TABLE 6 Crystal data and structure refinement for compound Y-FTZB-MOF(2) Identification code 2 Empirical formula C₅₂ H₁₈ F₆ N₂₆ O₇₈ Y₆Formula weight 2902.38 Temperature 100(2) K Wavelength 1.54178 Å Crystalsystem, space group Cubic, Fm-3m Unit cell dimensions a = 23.4365(4) Åalpha = 90 deg. b = 23.4365(4) Å beta = 90 deg. c = 23.4365(4) Å gamma =90 deg. Volume 12873.0(4) Å³ Z, Calculated density 4, 1.498 Mg/m³Absorption coefficient 4.527 mm⁻¹ F(000) 5696 Crystal size 0.10 × 0.10 ×0.10 mm Theta range for data collection 5.34 to 63.48 deg. Limitingindices −27 <= h <= 25, −18 <= k <= 27, −17 <= l <= 10 Reflectionscollected/unique 5335/575 [R(int) = 0.0313] Completeness to theta =63.48 97.0% Absorption correction Semi-empirical from equivalents Max.and min. transmission 0.6603 and 0.6603 Refinement method Full-matrixleast-squares on F² Data/restraints/parameters 575/69/88 Goodness-of-fiton F² 1.052 Final R indices [I > 2sigma(I)] R₁ = 0.0395, wR₂ = 0.1160 Rindices (all data) R₁ = 0.0414, wR₂ = 0.1183 Largest diff. peak and hole1.849 and −0.597 e.Å⁻³

TABLE 7 Crystal data and structure refinement for compound Tb-TZB-MOF(3) Identification code 3 Empirical formula C₄₈ H₃₂ N₂₄ O₅₈ Tb₆ Formulaweight 2826.43 Temperature 100(2) K Wavelength 1.54178 Å Crystal system,space group Cubic, Fm-3m Unit cell dimensions a = 23.5195(5) Å alpha =90 deg. b = 23.5195(5) Å beta = 90 deg. c = 23.5195(5) Å gamma = 90 deg.Volume 13010.2(5) Å³ Z, Calculated density 4, 1.439 Mg/m³ Absorptioncoefficient 16.428 mm⁻¹ F(000) 5336 Crystal size 0.10 × 0.10 × 0.10 mmTheta range for data collection 5.32 to 67.93 deg. Limiting indices −26<= h <= 22, −20 <= k <= 18, −22 <= l <= 27 Reflections collected/unique10330/624 [R(int) = 0.0380] Completeness to theta = 65.93 99.0%Absorption correction Semi-empirical from equivalents Max. and min.transmission 0.2904 and 0.2904 Refinement method Full-matrixleast-squares on F² Data/restraints/parameters 624/1/64 Goodness-of-fiton F² 1.086 Final R indices [I > 2sigma(I)] R₁ = 0.0340, wR₂ = 0.1028 Rindices (all data) R₁ = 0.0343, wR₂ = 0.1031 Largest diff. peak and hole1.161 and −0.493 e.Å⁻³

TABLE 8 Crystal data and structure refinement for compound Tb-FTZBP-MOF(4) Identification code 34 Empirical formula C₈₄ H₄₂ F₆ N₂₄O₂₆Tb₆Formula weight 2870.94 Temperature 200(2) K Wavelength 0.71073 Å Crystalsystem, space group Cubic, Fm-3m Unit cell dimensions a = 29.5957(3) Åalpha = 90 deg. b = 29.5957(3) Å beta = 90 deg. c = 29.5957(3) Å gamma =90 deg. Volume 25923.0(5) Å³ Z, Calculated density 4, 0.736 Mg/m³Absorption coefficient 1.651 mm⁻¹ F(000) 5464 Crystal size 0.20 × 0.20 ×0.20 mm Theta range for data collection 3.58 to 28.27 deg. Limitingindices −23 <= h <= 29, −30 <= k <= 8, −21 <= l <= 37 Reflectionscollected/unique 6198/1586 [R(int) = 0.0289] Completeness to theta =27.0 99.0% Absorption correction Semi-empirical from equivalents Max.and min. transmission 0.7336and 0.7336 Refinement method Full-matrixleast-squares on F² Data/restraints/parameters 1586/50/89Goodness-of-fit on F² 1.072 Final R indices [I > 2sigma(I)] R₁ = 0.0236,wR₂ = 0.0715 R indices (all data) R₁ = 0.0264, wR₂ = 0.0724 Largestdiff. peak and hole 1.128 and −0.532 e.Å⁻³

TABLE 9 Crystal data and structure refinement for compound Y-FTZBP-MOF(5) Identification code 5 Empirical formula C₈₄ H₄₂ F₆ N₂₄O₂₆Y₆ Formulaweight 2450.88 Temperature 100(2) K Wavelength 1.54178 Å Crystal system,space group Cubic, Fm-3m Unit cell dimensions a = 29.447(3) Å alpha = 90deg. b = 29.447(3) Å beta = 90 deg. c = 29.447(3) Å gamma = 90 deg.Volume 25535(4) Å³ Z, Calculated density 4, 0.638 Mg/m³ Absorptioncoefficient 2.074 mm⁻¹ F(000) 4840 Crystal size 0.20 × 0.20 × 0.20 mmTheta range for data collection 6.01 to 65.64 deg. Limiting indices −34<= h <= 24, −34 <= k <= 34, −23 <= l <= 33 Reflections collected/unique20849/1148 [R(int) = 0.0198] Completeness to theta = 65.64 98.3%Absorption correction Semi-empirical from equivalents Max. and min.transmission 0.6818 and 0.6818 Refinement method Full-matrixleast-squares on F² Data/restraints/parameters 1148/71/89Goodness-of-fit on F² 1.059 Final R indices [I > 2sigma(I)] R₁ = 0.0337,wR₂ = 0.1010 R indices (all data) R₁ = 0.0340, wR₂ = 0.1016 Largestdiff. peak and hole 0.675 and −0.283 e.Å⁻³

TABLE 10 Crystal data and structure refinement for compound Tb-FBPDC-MOF(6) Identification code 6 Empirical formula C₈₄ H₄₂ F₆ O₃₈ Tb₆ Formulaweight 2726.70 Temperature 100(2) K Wavelength 1.54178 Å Crystal system,space group Cubic, Fm-3m Unit cell dimensions a = 27.5127(12) Å alpha =90 deg. b = 27.5127(12) Å beta = 90 deg. c = 27.5127(12) Å gamma = 90deg. Volume 20825.7(16) Å³ Z, Calculated density 4, 0.870 Mg/m³Absorption coefficient 10.186 mm⁻¹ F(000) 5176 Crystal size 0.10 × 0.10× 0.10 mm Theta range for data collection 2.78 to 63.44 deg. Limitingindices −26 <= h <= 31, −29 <= k <= 31, −26 <= l <= 31 Reflectionscollected/unique 20823/917 [R(int) = 0.0442] Completeness to theta =63.44 99.6% Absorption correction Semi-empirical from equivalents Max.and min. transmission 0.4290 and 0.4290 Refinement method Full-matrixleast-squares on F² Data/restraints/parameters 917/38/59 Goodness-of-fiton F² 1.051 Final R indices [I > 2sigma(I)] R₁ = 0.0402, wR₂ = 0.1105 Rindices (all data) R₁ = 0.0420, wR₂ = 0.1125 Largest diff. peak and hole0.839 and −0.716 e.Å⁻³

TABLE 11 Crystal data and structure refinement for compoundTb-DFBPDC-MOF (7) Identification code 7 Empirical formula C₈₄ H₃₆ F₁₂O₄₆Tb₆ Formula weight 2962.65 Temperature 100(2) K Wavelength 1.54178 ÅCrystal system, space group Cubic, Fm-3m Unit cell dimensions a =27.4756(7) Å alpha = 90 deg. b = 27.4756(7) Å beta = 90 deg. c =27.4756(7) Å gamma = 90 deg. Volume 20741.6(9) Å³ Z, Calculated density4, 0.949 Mg/m³ Absorption coefficient 10.332 mm⁻¹ F(000) 5624 Crystalsize 0.15 × 0.15 × 0.15 mm Theta range for data collection 4.55 to 67.93deg. Limiting indices −23 <= h <= 31, −32 <= k <= 29, −28 <= l <= 31Reflections collected/unique 5524/5524 [R(int) = 0.000] Completeness totheta = 66.60 98.7% Absorption correction Semi-empirical fromequivalents Max. and min. transmission 0.3063 and 0.3063 Refinementmethod Full-matrix least-squares on F² Data/restraints/parameters5524/4/38 Goodness-of-fit on F² 1.051 Final R indices [I > 2sigma(I)] R₁= 0.0732, wR₂ = 0.2048 R indices (all data) R₁ = 0.0768, wR₂ = 0.2085Largest diff. peak and hole 1.137 and −1.339 e.Å⁻³

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Otherembodiments are within the scope of the following claims.

What is claimed is:
 1. A metal-organic framework composition,comprising: one or more of a hexanuclear metal cluster, each hexanuclearmetal cluster comprising one or more of a rare earth metal ion; and oneor more of a bidentate ligand.
 2. The composition of claim 1, whereinthe hexanuclear metal cluster is characterized by the formula[RE₆(μ₃-OH)₈(O₂C—)₆N₄C—)₆].
 3. The composition of claim 1, wherein thehexanuclear metal cluster is characterized by the formula[RE₆(μ₃-OH)₈(O₂C—)₁₂].
 4. The composition of claim 1, wherein the rareearth metal ion comprises one or more of cerium, dysprosium, erbium,europium, gadolinium, holmium, lanthanum, lutetium, neodymium,praseodymium, promethium, samarium, scandium, terbium, thulium,ytterbium, or yttrium.
 5. The composition of claim 1, wherein thebidentate ligand includes one or more of a carboxylate, tetrazolate,triazolate, or pyrazolate.
 6. The composition of claim 1, wherein thebidentate ligand comprises one or more of the following ligands:2-fluoro-4-(1H-tetrazol-5-yl)benzoate (FTZB),4-(1H-tetrazol-5-yl)benzoate (TZB),3-fluoro-4′-(2H-tetrazol-5-yl)biphenyl-4-carboxylate (FTZBP),3-fluorobiphenyl-4,4′-dicarboxylate (FBPDC), or3,3′-difluorobiphenyl-4,4′-dicarboxylate (DFBPDC).
 7. The composition ofclaim 1, wherein the bidentate ligand has two anionic binding groups. 8.The composition of claim 7, wherein the two anionic binding groups arethe same.
 9. The composition of claim 7, wherein the two anionic bindinggroups are different.
 10. The composition of claim 7, wherein the twoanionic binding groups are linked by one or more of an aromatic group orhydrophobic group.
 11. The composition of claim 1, wherein thehexanuclear metal cluster and bidentate ligand associate to form aface-centered cubic topology.
 12. A method of making a metal-organicframework, comprising: contacting one or more of a hexanuclear metalcluster, each hexanuclear metal cluster comprising one or more of a rareearth metal ion, with one or more of a bidentate ligand.
 13. The methodof claim 12, wherein the hexanuclear cluster is characterized by theformula [RE₆(μ₃-OH)₈(O₂C—)₆N₄C—)₆].
 14. The method of claim 12, whereinthe hexnuclear metal cluster is characterized by the formula[RE₆(μ₃-OH)₈(O₂C—)₁₂].
 15. The method of claim 12, wherein the rareearth metal ion includes one or more of cerium, dysprosium, erbium,europium, gadolinium, holmium, lanthanum, lutetium, neodymium,praseodymium, promethium, samarium, scandium, terbium, thulium,ytterbium, or yttrium.
 16. The method of claim 12, wherein the bidentateligand includes one or more of a carboxylate, tetrazolate, triazolate,or pyrazolate.
 17. The method of claim 12, wherein the bidentate ligandcomprises one or more of the following ligands:2-fluoro-4-(1H-tetrazol-5-yl)benzoate (FTZB),4-(1H-tetrazol-5-yl)benzoate (TZB),3-fluoro-4′-(2H-tetrazol-5-yl)biphenyl-4-carboxylate (FTZBP),3-fluorobiphenyl-4,4′-dicarboxylate (FBPDC), or3,3′-difluorobiphenyl-4,4′-dicarboxylate (DFBPDC).
 18. The method ofclaim 12, wherein the bidentate ligand has two anionic binding groups.19. The method of claim 18, wherein the two anionic binding groups arelinked by one or more of an aromatic group or hydrophobic group.
 20. Themethod of claim 13, wherein the hexanuclear metal cluster and bidentateligand associate to form a face-centered cubic topology.